(1) Filed of the Invention
The present invention lies in the field of systems for navigating and managing the flight of an aircraft that covers, among other functions, the functions of preparing a flight plan and of generating a flight path for the aircraft.
The present invention relates to a method of calculating a safe path from the current position of an aircraft to an attachment point, and also to a device for performing the method.
(2) Description of Related Art
It should be observed that the term “flight plan” is used to designate a theoretical route to be followed by an aircraft, which theoretical route joins together a plurality of successive waypoints.
In addition, the term “path” is used to mean the track to be followed by the aircraft in order to follow the flight plan, which track is as close as possible to the theoretical route defined by the flight plan. The path is made safe and takes account of the performance and of the capabilities of the aircraft, and also of the proximity of the terrain and the presence of any obstacles.
Before each flight of an aircraft, the crew of the aircraft generally draws up a flight plan for the entire flight, with an initial route being defined by the flight plan.
Nevertheless, during the flight, the aircraft may be diverted and thus leave the initial route under particular circumstances. For example, the aircraft may be caused to leave its initial route in order to assist people or indeed to load equipment. The return path of the aircraft over the initial route then needs to be planned during a flight while using such equipment as is available to the crew of the aircraft. Furthermore, in the context of military missions, the aircraft may have only a short time in which to rejoin its initial route. The crew then has little time to change target and rejoin the initial route.
Likewise, during reconnaissance missions, the flight plan as prepared has a go flight itinerary from a starting base to a point of entering the reconnaissance zone, and for a return flight itinerary from an exit point from the reconnaissance zone back to base. While overflying the reconnaissance zone, a flight plan may also be established. Nevertheless, such a flight plan may be sparse or even non-existent, due to lack of knowledge about the terrain in that zone. Furthermore, this flight plan concerning overflying the reconnaissance zone may need to be changed during the flight, in particular in the context of military reconnaissance.
Furthermore, in the context of military missions, the path of the aircraft often needs to involve low altitude flight in order to limit detection and vulnerability of the aircraft. Drawing up an accurate flight plan is then essential in order to guarantee that this low altitude path is safe.
Likewise, drawing up an accurate flight plan is particularly advantageous during poor weather conditions that reduce the pilot's visibility.
The navigation systems that are nowadays to be found on board aircraft, and in particular on-board rotary wing aircraft, can enable an aircraft to return to a specified point starting from its current position.
For example, such conventional navigation systems propose a function known as the “direct-to” function, which consists in proposing a path constituted by a single substantially straight track directly connecting the current position of the aircraft to a point that is specified manually by the crew of the aircraft. The path is a path that is plane in two dimensions. This path can be established quickly. However, this path takes no account of the topography of the terrain or of the presence of obstacles. As a result, this “direct-to” function is not safe and is therefore not suitable for all types of terrain, in particular in the presence of a hill, of obstacles, or indeed of mountainous relief.
An improvement to this “direct-to” function consists in constructing a genuine three-dimensional path comprising a substantially straight and horizontal main track connecting a first vertical line passing through the current position of the aircraft to a second vertical line passing through the designated point. The track is positioned at a height relative to the ground that corresponds to the maximum height of the terrain underlying the track, plus a safety margin. The path also has a first track and a last track that are substantially vertical, respectively connecting the current position of the aircraft to the main track and the main track to the designated point.
This improvement has the advantage of proposing a genuine 3D path that is safe relative to the terrain overflown by the aircraft. Nevertheless, this safe 3D path is not optimized. In particular, this safe 3D path allows for relief or obstacles to be passed solely by passing over them, but does not make any proposal for going round them on a horizontal path that might be better suited to the capabilities and the performance of the aircraft or to the discretion that is required for military missions.
Furthermore, aircraft fitted with sophisticated navigation systems have the option of modifying the initial route defined by the flight plan or of creating a new route for the aircraft in accurate manner. Nevertheless, only a horizontal component of the path of the aircraft can be created or modified, since this function is available only in two dimensions. This function also represents a considerable workload for the crew of the aircraft, since there can sometimes be as many as fifty operations to perform. Specifically, a plurality of successive waypoints need to be inserted manually on a map display in order to define the new route for the aircraft. Drawing up this new route thus takes a relatively long time.
Furthermore, Document FR 2 847 553 describes a method that may be considered as an extension of the “direct-to” function when the designated point lies on a predetermined route. Specifically, that method avoids the need for the crew to designate the designated point manually, since it is defined automatically by the method as the point of intersection between extending the current speed vector of the aircraft and the predetermined route. In order to engage the method, the pilot only needs to direct the aircraft in terms of its speed vector to the point where the pilot seeks to return to the predetermined route. The method defines a path having a straight first segment from the current position of the aircraft and a curvilinear second segment constituting a junction between the straight first segment and the initial route. Nevertheless, that path is situated in a horizontal plane that contains the current position of the aircraft and the designated point, and it is therefore not safe and suitable for all types of terrain.
Also known is Document FR 2 928 726, which describes a method of calculating a junction path between an exit point from a primary route and an entry point to a secondary route. The flight path following characteristics such as the speed of the aircraft, its altitude, and its turning capability are different for the primary and secondary routes. That method defines a capture point on the secondary route, upstream from the entry point. The aircraft must have acquired the path-following characteristics for the secondary route by the time it passes through the capture point or close thereto in order to be able to follow the secondary route as it goes through the entry point. The junction path is formed by tracks defined in compliance with the ARINC 424 standard, and for example a track may for example be defined using the “direct-to” function.
In both those documents, the path for rejoining an existing route is defined without taking account of the topography of the terrain or the presence of obstacles. The path therefore cannot be considered as being a safe path.
Furthermore, Document CN 104516354 describes a method of determining return itineraries for a pilot-less helicopter, with three different return itineraries being defined.
Finally, Documents FR 2 947 370 and EP 1 614 086 describe a method of preparing and following a flight plan between two passage points. That method makes it possible in particular to define a path corresponding to the flight plan, while taking account of the topography of the terrain. The path is subdivided into a plurality of horizontal tracks, each track being arranged above the underlying zone of the terrain.
By way of example, according to Document EP 1 614 086, it is verified that each track does not interfere with the terrain, or where applicable an operator is warned so that each interfering track can be modified and positioned at a safe altitude higher than the highest point of the underlying terrain.
According to Document FR 2 947 370, a “sheet-laying” method enables each horizontal track to be arranged directly at a safe altitude. With that path, the aircraft can thus fly as close as possible to the terrain in safe manner without any risk of interference. That path may also be referred to as “terrain flight” or “vertical contour flight”.